This invention relates to slicing machines for slicing food products, particularly slicing cheese, meat and pressed or moulded meat products.
A slicing machine for such products comprises a rotating blade which either has a spiral cutting edge or has a circular cutting edge and is mounted for planetary motion, and means to feed the product towards the blade so that upon each revolution or each gyration of the blade one clise is cut from the face of the product. The means to feed the product may be a continuous conveyor but usually the slicer includes a fixed platform on which the product is placed and a feeding head which engages the rear face of the product and which urges the product towards the blade. The feeding head is moved by a hydraulic ram or by a leadscrew driven by a stepping or variable speed electric motor.
The product may be moved forward at a constant speed and since the rotation or gyration of the blade is also constant, each successive slice is of substantially uniform thickness but each slice is inclined to the direction of movement of the product. This has a disadvantage that wedge-shaped slices of meat are cut from the first and last slices and whenever the cutting is interrupted. Such wedge-shaped slices are significantly underweight. Because of this it is desirable to move the product stepwise each time the cutting edge of the blade is out of contact with the product. This technique is more commonly used where the slices fo product are required to be thicker and where the product is comparatively firm. As the rear face of the product is moved forward in a stepwise fashion it is moved forwards rather suddenly and this results in a shock wave being transmitted from the rear face of the product along its length. This shock wave or vibration passing down the length of product can cause the front face to move in an irregular fashion whilst the next slice is being cut from it. This leads to the slices having an irregular thickness and a very irregular weight. This is particularly true of meat and meat products that are relatively soft and obviously particularly noticeable where very th in slices of product are cut. An example of this is where the product is ham or sausage. It is also possible for the product to be urged forwards stepwise so rapidly that once the block of meat or meat product starts to move it continues to move and pulls away from the feeding head, so causing further damage to it.
A slicing machine is usually required to produce groups of slices and this may be achieved by having the slicing machine discharge onto a constant speed conveyor and then interrupting the feed of the product towards the blade for a period of time, each time a predetermined number of slices have been cut from its face, but, more usually, the conveyor downstream from the slicing machine is a jump conveyor. In this case, the conveyor moves forward at a first speed whilst slices are cut from the product at a uniform rate and then, after the number of slices required for each group have been cut, the jump conveyor moves at a second speed, considerably faster than the first speed, and then returns to the first speed. In this way, the slices are cut at a uniform rate but the increase in speed of the jump conveyor after each group of slices has been cut results in a series of groups of slices being formed on the jump conveyor.
Such slicing machines are usually provided at the upstream ends of a packaging line and whilst the packaging line is usually arranged to run on a continuous basis, it is sometimes necessary to interrupt the slicing operation if, for example, the packaging line is under-manned or there is some interruption in a downstream packaging machine. Under such circumstances it is necessary to stop the operation of the slicing machine halfway through a piece of product. Normally, this is achieved by stopping the feed of the product towards the blade but this invariably occurs in the middle of a sliced group so that group is not complete. Also, upon restarting the slicing machine the first group produced by the slicing machine is also often incomplete. When the feed of product towards the blade is operated continuously, stopping the feeding head during its travel results in both the last slice that is cut before the interruption and the first slice that is cut after the interruption being wedge-shaped and the weight of the group containing those slices being less than the standard pack weight.